Process of sweetening petroleum hydrocarbons



Patented Sept. 17, 1935 PATENT OFFICE PROCESS or swssrsmo PETROLEUM nrnaooaanons Ernest F. Pevere, Beacon, N. Y., assignor to The Texas Company, New York, N. Y., a corporation oi Delaware Serial No. 624,350

No Drawing. Application July 23, 1932,

8Clalms.

This invention relates to the treating of hydrocarbon oils and more particularly to a process of treating such oils as the lighter derivatives of petroleum or the light hydrocarbons prepared by the pyrolytic decomposition of petroleum. These hydrocarbon oils may include hydrocarbons within the boiling ranges of gasoline and kerosene.

Most light mineral oil distillates such as gasoline or kerosene contain sulfur compounds which impart disagreeable odors to the oil and whose presence is indicated by a positive reaction to the doctor test. This test consists in agitating the oils with an alkaline solution of an alkali metal plumbite, such as sodium plumbite, prepared by dissolving lead oxide in an excess of sodium hydroxide. After allowing the mixture to settle, any discolorization produced in the oil or in the aqueous solution or at the oil solution interface indicates that the oil contains undesirable sulfur compounds and it is designated as being positive to the doctor test or sour. A corresponding lack of color indicates that the oil is negative to the doctor test or "sweet.

In order that oils such as gasoline or kerosene which are sour may be rendered sweet, it is common practice to treat the oil with an alkaline solution of sodium plumbite during which treatment free sulfur is usually added to the oil. This operation may be typified by the following equations which illustrate the reactions:

While the ordinary method of treating with sodium plumbite and sulfur is at present generally recognized as being the most efficient as regards the high quality of the product resulting from its use, the exceptionally high cost introduces a serious disadvantage. It is known that in the case of high sulfur naphthas, as much as one pound of litharge per barrel of gasoline may be consumed in the operation.

Several new methods of sweetening have been proposed in order to circumvent the difficulties of an alkali plumbite-sulfur method of treating. Most of these methods feature a vigorous direct oxidation of the sulfur compounds by means of oxidizing agents. The difficulties encountered with these methods are usually traceable to the lack of control over the oxidizing action and it is quite probable that the oxidation is not limited to the undesirable sulfur compounds but also extends to an oxidation of those unsaturated bodies present in the oils which confer desirable characteristics to the hydrocarbon mixture in which they are present. An oxidation of such unsaturated compounds may result in undesirable reductions in color stability and decreases in the anti-knock values of the finished products.

By the application of the herein disclosed in- 10 vention, it is possible to subject sour hydrocarbons, that is, hydrocarbons containing mercaptan compounds, to a controlled oxidation which permits of the complete conversion of the mercaptans to the corresponding disulfides without in any way affecting the color and gum stability of the naphtha with which the mercaptans are associated.

I have discovered that when hydrocarbons containing sulfur compounds of the mercaptan se- 2 ries are treated in the presence of air with an alkaline solution containing a comparatively small quantity of phenolic bodies, that the mercaptans are readily transformed into the corresponding disulfide compounds. discovered that the rate of the transformation of the mercaptans into the disulfides may be greatly accelerated by employing benzenoid compounds containing at least two substituted groups of which one at least is preferably an amino or hydroxyl grouping. Similarly, I have noted that by using oxidizing agents in conjunction with this treating agent that the efliciency of the treating solution is increased to a considerable extent.

Naphthas suitable for use as motor fuel when treated in accordance with my invention, are stable to light and storage and the time necessary for reaction is considerably less than is the case when the usual sodium plumbite-sulfur method of treating is employed. To explain the extraordinary results obtained with this treating solution, I advance the following theoretical explanation to the correctness of which I do not intend to limit myself. When an unsweetened naphtha is agitated with a solution of sodium hydroxide, there is the usual reaction of the lower molecular weight mercaptans with the sodium hydroxide which results in the production of sodium mercaptides. The high molecular weight mercaptans however are only I have further 25 '7 reacted upon to a slight degree by the sodium hydroxide. f the naphtha is agitated for a considerable. le gth of time with the sodium hydroxide, it will be observed that some of the higher molecular weight mercaptans may be transformed into the corresponding disulflde compounds. I have discovered that the latter reaction occurs only in those cases where the original naphtha contains phenolic bodies. By purposely increasing the concentration of the phenolic bodies present in the treating solution by adding thereto small percentages of phenols, it has been noted that a more extensive and a more rapid transformation of the higher molecular weight mercaptans into the corresponding' disulfldes takes place.

By carrying out this reaction with the above treating solution in the presence of air or a mild oxidizing agent, the rate of extent of the sweetening is still further increased. Upon examination of such a treating solution after its use, it is found that the phenols are present in their original form from which it may be concluded that the phenolic bodies serve merely as catalytic agents in the conversion of the mercaptans into disulfldes.

The catalytic activities of the various phenolic compounds appear to be dependent upon the structural characteristics of these compounds. The most reactive of the catalysts are hydroquinone, catechol and p-amino-phenol. Compounds such as o-amino-phenol, ortho and para phenol sulfonic acid, phenylene diamine, alpha naphthol sulfanilic acid, and aniline also appear to display this characteristic.

An explanation of the mechanism of the treating reaction may be arrived at when it is considered that hydroquinone readily reacts with oxygen to yield either quinone or quinhydrone. These reactions appear in the following equations:

The quinhydrone which is formed in accordance with the second equation is a double compound of hydroquinone and quinone. Its formation is readily brought about by subjecting hydroquinone to the action of oxygen or other mild oxidizing agents such as extremely dilute peroxides or permanganates. Both quinone and quinhydrone react with mercaptans to form the corresponding disulfides. The reactions which take place may be set forth as follows:

It is therefore possible to continuously transform mercaptans into the corresponding disulfldes by treating them with alkaline solutions of quinone or quinhydrone which have been formed by oxidizing hydroquinone with oxygen or mild oxidizing agents.

In the application of my invention, it may be desirable in certain types of operations, for example, when using sulfanilic acid, phenol sulfonic acid and aniline, to combine the oxidizing agent which may be a peroxide or pennanganate with the alkaline solution of the catalytic reagent although for the most of the applications, it may be found desirable to activate the solution by subjecting it to treatment with air. As a specific example of the practice of my inven-' tion, I give below the constitution of a treating solution which may be used for sweetening a naphtha containing mercaptans ordinarily not affected by sodium hydroxide which will sweeten a quantity of naphtha equivalent to times its volume.

tion

350 lbs. of hydroquinone This solution may be activated by agitating it with air or by introducing into it a small percentage of hydrogen peroxide, sodium peroxide or" similar oxidizing agents. The solution after use will have deteriorated only insofar as the hy-v droquinone will have been reformed by the reduction of the quinhydrone as the result of the oxidation of the mercaptans to the disulfldes. The solution may be reactivated by adding further quantities of oxidizing agents or by resub- Jection to the action of air,

It is apparent that my invention readily lends itself to incorporation in a continuous treating system in which case the hydrocarbon oil to be sweetened'is intimately mixed with the appropriate quantity of activated treating solution and agitated therewith. After thorough agitation, the mixture may be conducted through one or more settling chambers where the velocity of flow is reduced to such a rate as to permit the separation of the oil from the treating solution. The separated oil may then be withdrawn while the treating solution is introduced into an activator where it is resubiected to the action of air. The reactivated solution may then be withdrawn and reused in the continuous treat- 50 bbls. of 15 Baum sodium hydroxide solu- I jecting the oil containing the mercaptans to reaction with an aqueous alkaline solution of a phenol.

2. The process of converting mercaptans present in a petroleum hydrocarbon oil into the corresponding disulfldes which comprises agitating the oil containing the mercaptans in the presence of air with an aqueous alkaline solution containing a phenol.

3. The process of converting mercaptans present in a petroleum hydrocarbon oil into disulfldes which comprises interacting the oil containing the mercaptans with an alkaline solution containing phenols and a mild oxidizing agent.

4. The process of sweetening petroleum hydrocarbons containing mercaptans which comprises agitating the hydrocarbons with an alkaline solution containing phenol and a mild oxidizing agent.

5. The process of converting mercaptans present in a petroleum hydrocarbon oil into disulfldes which comprises reacting the oil containingthe mercaptans with an alkaline solution containing polyhydric phenols and a mild oxidizing agent.

6. The process of treating naphthas containing mercaptans with catalytic alkaline solutions which comprises subjecting an alkaline solution containing a dihydroxy phenol to a mild oxidizing reaction, commlngling and reacting the mercaptan-containing naphtha with the oxidized alkaline solution whereby the mercaptans are transformed into the corresponding disulfides, separating the treated naphtha from the alkaline treating solution, drawing ofi the treated naphthe. and cyclically returning the alkaline solution to further mild oxidation.

7. The step in the process of sweetening pe- 10 troieum hydrocarbons consisting in agitating the hydrocarbons with an alkaline solution containing a small percentage of hydroquinone, which solution has been activated by previously treating it with a mild oxidizing agent.

8. The process of sweetening petroleum hydrocarbons containing mercaptans which comprises agitating the hydrocarbons with an alkaline solution containing an amino phenol and a mild oxidizing agent.

ERNEST F. PEVERE. 

